Eukaryotic Phylogeny & Land Plant Adaptations PDF

# Archaeplastida - Contains descendants from endosymbiotic cyanobacteria with chloroplasts. # Excavata # Amoebozoa # SAR - Also known as glaucocystophytes or glaucocystoids. - Are a small group of unicellular algae found in freshwater and moist terrestrial environments. - Less common today than the...

# Archaeplastida - Contains descendants from endosymbiotic cyanobacteria with chloroplasts. # Excavata # Amoebozoa # SAR - Also known as glaucocystophytes or glaucocystoids. - Are a small group of unicellular algae found in freshwater and moist terrestrial environments. - Less common today than they were during the Proterozoic. # Opisthokonta ## Adaptations Enabling the Move to Land - In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out. - The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens. - Land presented challenges: a scarcity of water and lack of structural support. ## Morphological and Molecular Evidence - Many characteristics of land plants also appear in a variety of algal clades, mainly algae. - However, land plants share multiple traits with charophytes which include: - Chlorophylls a and b - Cellulose - Structure of flagellated sperm - Formation of sporopollenin ## Land plants evolved from green algae - Green algae/ Glucophyta relatives called Charophytes appear to be the closest relatives of land plants. - 290,000 living species of living plants. - Comparisons of both nuclear and chloroplast genes point to charophytes as possibly the closest living relatives of land plants. - Note that land plants are not necessarily descended from modern charophytes, but share a common ancestor with modern charophytes. ## Four Key Traits - Four key traits appear in nearly all land plants but are absent in the charophytes: - Alternation of generations (with multicellular, dependent embryos) - Walled spores produced in sporangia - Multicellular gametangia - Apical meristems - Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients. ## Alternation of Generations and Multicellular, Dependent Embryos - Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations. - The gametophyte is haploid and produces haploid gametes by mitosis. - Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis. - Land plants are called embryophytes because of the dependency of the embryo on the parent. ## Sporophyte vs Gametophyte - The diploid generation is called the sporophyte. - The haploid generation is called the gametophyte. - As plants evolved, the sporophyte tissue dominated. ## Derived Traits of Plants - The accumulation of derived traits that facilitated survival on land may have opened the way to its colonization by plants. - Protection from desiccation (cuticle). - Protection from predators (secondary compounds). - And eventually, transport of water, minerals and nutrients (Xylem (tracheids) and phloem, in other words, plumbing). ## Superkingdom Archaeplastida - Viridiplantae includes the largest amount of genetic diversity among plant-like organisms. The image also shows a diagram of the evolutionary tree of eukaryotes, outlining the different lineages and their relationships to one another. This phylogenetic tree provides a visual representation of the relationships between different eukaryotic groups. It also shows images of different types of gametophytes, demonstrating the differences between primitive and vascular plants.